New bronchodilators-3:: Synthesis of benzimidazo [1,2-c]-quinazolin-6 (5H)-ones and their thio analogues

Synthesis of some new benzimidazo [1,2-c] quinazolin-6(5H)-ones (IV) and their thio analogues (III) has been accomplished. The key Intermediates, 2-(2-aminophenyl) benzimidazoles (II) were obtained by direct condensation of substituted anthranilic acids (I) with o-phenylenediamine using polyphosphoric acid (PPA) as dehydrocyclizing agent. Benzimidazo[1,2-c] quinazolin-6(5H)-thiones (III) were obtained by condensing 2-(2-aminophenyl) benzimidazole (II) with carbon disulfide (CS2) and their corresponding oxo analogues IV were synthesized by the oxidation of III, with alkaline KMnO4. The structure of the compounds III and IV have been established on the basis of their elemental analyses and spectral (IR, H-1 NMR and Mass) data. The bronchodilatory activity of compounds IIIa and IVa is reported using in vitro and in vivo animal models.